There has already been known, in particular according to the patent application FR-A-2 458 857 an electronic display arrangement including a set of modules which are respectively constituted either by the electrodes of a liquid crystal cell, or by electro-luminescent diodes and which have the form of straight line segments arranged adjacent to one another and abutting by lines and by columns.
On the graphical plan, this arrangement does not give entire satisfaction since it enables display only of "stick" characters, that is to say, under the form of strokes joined to one another.
Furthermore, this arrangement is considerably limited since the modules do not permit the indiscriminate display either of lower case forms or capitals.
Furthermore, the patent application EP 0 46 285 describes a display arrangement of another type, that is to say, structured essentially under the form of a point matrix having n lines and p columns (n being equal to 5 and p equal to 3, in this example).
The pixels of this matrix, that is to say the most elementary patterns each of which forms an electrode individually addressable, have been modified relative to the pixels of the most standard point matrices solely with the purpose of increasing the resolution. Thus, those who conceived such matrix while wishing absolutely to maintain the qualities of low order matrices (typically 5.times.3) have attempted to increase the number of pixels. At this epoch, they thus started off naturally from a standard material form including rectangular pixels and more particularly square pixels, by definition all identical, and distributed in a homogeneous fashion. The purpose which they set themselves has led to division of said pixels in four, in cutting almost all of them up in a quasi identical manner by means of two diagonals. The resulting structure is thus made up essentially of several repeated groups, each composed of four isosceles triangles. In observing the contours or the envelope of such groups, one readily finds anew the aspect of the original rectangles, the junction of which I constitutes the pattern or grid of the matrix.
It is thus noted that the structure of this arrangement remains within a concept which is very regular and-ordered, with a strict and almost identical repetition of the groups and pixels responding to the definition of material type displays.
This special conception of electro-optical displays exhibits major difficulties. Effectively, the form of the displayable characters is determined from the outset by the material arrangement of the electrodes or pixels. Thus, starting out from a plan which is rigid and determined, the user has as his only possibility to select within such given plan the pixels which are at his disposal in order to obtain a letter or a digit. It is thus impossible for him to visualize stylized characters since the capacities of the arrangements are confined within the original pattern.
Consequently, although the arrangement proposed in this patent application answers the desires of increasing the resolution of display arrangements of the material type by increasing the number of pixels, it is understood that it is very limited. Effectively, users and consequently buyers of these arrangements henceforth seek out characters of the most appealing form possible, close to a special type or to a personalized writing.
Patent application EP 0 780 685, in particular in its last embodiment, responds partially to this problem in furnishing an arrangement having a different conception. The first purpose being to improve the design of the characters, the conceivers of such arrangement have started off, no longer from an imposed plan of electrodes, but from the result to be obtained, namely from the letters and numbers themselves, in order to conform the electrodes solely thereafter.
This is why the pixels as obtained are irregularly formed and arranged in a disordered manner without systematic repetition in lines and columns, such pixels having among themselves different contours for the most part.
This type of arrangement ms called a "mosaic" because of its structure of composite aspect formed from numerous pixels having heterogeneous contours (rounded off, rectilinear, in angles . . . ), but complementary and in concordance therewith nesting into one another. It is noted that one does not take into account a logical and uniformly spread distribution of the pixels or electrodes over the entire surface of the arrangement, in contrast to the material structures defined hereinabove. Such type of device is related to the arrangement of pieces of coloured glass which one finds in ancient stained glass windows in religious edifices, in particular in the West.
This arrangement exhibits major difficulties.
Initially, it is noted that in an irremediable manner the fact of stylizing characters leads to increasing the number of pixels which raises the price of the finished and equipped arrangement in a very substantial manner to the extent where it is necessary to associate it with electronic circuits which are more sophisticated and "heavier".
Furthermore, the characters obtained suffer from poor definition and they show, as will be explained hereinafter, defects formed by points.
Effectively, and as is shown very schematically on FIG. 2 of the attached drawings, there appear on the displayed characters such as the "A" shown, points or marks (referenced 10), such defects affecting in particular the aspect and thus the design quality of said characters.
Furthermore, "noise" lines such as that referenced on FIG. 2, appear at the side of, indeed within the characters.
Effectively, each elementary pattern being constituted by an electrode which is electrically insulated from the neighbouring electrodes, it is necessary to couple each pattern to the electronic control system by its own electrical connection.
Such connections are formed by tracks which are structured, as the electrodes, by a photo-lithographic process on a substrate covered by a conductive layer, and they are consequently apt to cause variations of the optical characteristics of the liquid crystal located between them and a portion of the counter-electrode. It is hence understood that such connections may appear on the cell at the same time as the alpha-numeric characters to be displayed, this contributing once again to a deterioration of the quality of the display.
To alleviate this, it has been proposed either to divide into several very fine branches 11a each of the connections where they overlap the counter-electrode in a manner to render them invisible (FIG. 2a) or to conceive a counter-electrode of extreme complication overlapping only the electrode and not the electrical connections.
In both cases, one obtains arrangements which are complicated to bring into being and as may well be understood, very expensive.
Furthermore, the arrangement according to such application EP 0 180 685, although providing a clear improvement in the form of the characters, remains still very limited since it does not enable visualization of lower case letters. It also shows the essential difficulty of having to be dimensioned as a function of the dimension of the digits and letters to be displayed. This dimension is thus set and may be modified only by changing the arrangement already installed in favour of another of different size.